My 2002 XJR has been exhibiting a CEL for a while, along with a rather intermittent “Restricted Performance” (RP) message. C0172 and C0175 were indicating both banks as “too rich”. After reading all I could to educate myself along with reading other fellows’ experiences, I thought something common to both banks must be the problem. Although the MAFS had been replaced only about a year ago as part of that nice $4,000.00 repair bill by this local British shop in SoCal, I still suspected the MAFS, so I removed it, inspected and cleaned it in spite of the fact that it was only a year old. Put it back in the car and P0172 and P0175 were gone and have not returned.
Then I had to resolve two more codes, P1638 and P1642. The main thing that I have learned about these codes is that they come up when there is a communication problem between the ECM and the instrument cluster. After carefully studying the circuit schematics I realized that we’re talking about only two wires that, on their way to the instrument cluster, they do go through a lighting module inside the tranny selector tower, but for now I just left that alone. I rather proceeded to just clean the ECM output connector pins (BTW, no humidity or water or signs of ever being wet in there) and the instrument cluster’s black connector pins, although I did clean the pins on the yellow connector, as well, just because. Put everything back and guess what? Yup, codes P1638 and P1642 were now gone as well, and still are. Oh, and the CEL is gone, too, of course (finally).
Uhh, the “Restricted Performance message is gone, as well, but I went too fast with this and I failed to identify which one of the two sets of codes is the one that got rid of the “RP” announcement. Probably it was the open lead(s).
I thought of adding this info here because this resolved these issues for me cheap and fast, meaning you don’t need to examine fuel trims or any expensive parts before you clean up those 20 years old connections.
Thank you Andy, so do I.
I’m actually thinking that cars (or the MAFS assy, itself) should feature a far more sophisticated air filtering system right in front of the MAFS sensors, so they won’t pick up contamination so fast. My MAFS is only 1 1/2 years old and careful examination with a good light and with an eye loop clearly showed oily dust coats over the sensing elements’ side that faces the incoming air flow, yet it was a new device just a year and a half ago (BTW, the air filter’s also that new). This told me that the sensor’s contaminated surface had lost some sensitivity so it was reporting less incoming air mass than was actually coming in, thus, “not enough air” means “too much fuel”, as in “too rich”, both banks. A good job with “MAFS cleaner” plus a can of clean/dry air spray made it look all clean and shiny. But, the fact that it has now been like three days without a recurring CEL tells me that it is obvious that cleaning up the sensor somehow got right in to the source of the problem, so I trust that it will last.
The temp sensor is more visible, but there’s also an airflow sensor in there.
Well, I thought about the ECM myself, but then I thought what’s the difference when you replace a bad battery, which also deprives the ECM of power for however long it takes for the new battery to get connected. So, actually nothing happened in this case and the car started right up immediately after, and it’s still running fine.
Well I looked at my original sensor.
The temperature sensor looked perfect on one side and scooted black on the other!
The 2 bar air flow didn’t look too bad.
All were cleaned.
I looked at the used sensor I had.
The temperature sensor looked ok, but the 2 bars were black. So they have been cleaned.
Thank you for your post.
I don’t have much hope, will have to see
But you haven’t, yet, tested it on the running engine, right?
Are you still getting left and right banks too rich codes?
Remember that I reported the same thing in regards to the temp sensor being dirty only on its incoming air wall.
Have you tried your other MAFS unit in the car yet?
I sure hope you clear this soon.
